Announcement

Collapse
No announcement yet.

First try at thread cutting

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Looking at the picture in post #9, you have a large gear attached to a small one on the same shaft, with the small one driving a big one. That's a typical step down arrangement used for a power feed (very fine feed to make a smooth cut). Many people leave it in this configuration whenever they are not threading.

    I suspect the seller did not bother to look for the change gears used for threading.


    Dan
    At the end of the project, there is a profound difference between spare parts and extra parts.

    Location: SF East Bay.

    Comment


    • #17
      Thanks for the replies, everyone. Sounds like my initial suspicion was correct, I need some change gears.

      Saw this on eBay. Anyone know if they'd work my lathe?

      http://m.ebay.com/itm/121866210679
      Last edited by Commander_Chaos; 01-17-2016, 08:42 AM.

      Comment


      • #18
        Also depending on what change gears you have, you need to figure out what thread per inch you are cutting. You may want to make sure your thread dial lines up with the same number before engaging the half nuts so that you know for sure you are cutting the same thread on each pass.

        Comment


        • #19
          Originally posted by quadrod View Post
          Also depending on what change gears you have, you need to figure out what thread per inch you are cutting. You may want to make sure your thread dial lines up with the same number before engaging the half nuts so that you know for sure you are cutting the same thread on each pass.
          The videos I've seen so far have said even number threads can be picked up on any line or number and odd number threads have to be picked up on just the number.

          Comment


          • #20
            Originally posted by Commander_Chaos View Post
            The videos I've seen so far have said even number threads can be picked up on any line or number and odd number threads have to be picked up on just the number.
            For purposes of practicing, if you pick a thread pitch that is an even multiple or divisor of the leadscrew pitch, you don't need to pay any attention to the thread dial.

            If the lathe leadscrew is 6 tpi, you should be able to cut 6, 12, 24 and maybe 2, 3 threads per inch without even having a thread dial.

            Dave

            Comment


            • #21
              Originally posted by Commander_Chaos View Post
              The videos I've seen so far have said even number threads can be picked up on any line or number and odd number threads have to be picked up on just the number.
              Nearly but not quite. Threads which are a multiple of the leadscrew (which I'm guessing is 8TPI) such as 8, 16, 24,etc can be picked up on any line or number. Threads such as 4, 12, 20 can be picked up on any number or any line, but you have to stick to lines or numbers, you can't mix them. After that, its simplest to stick to the same line or number.

              Those gears on ebay. Assuming the seller is correct that they are for a 9" Southbend, and he will confirm that they have all their teeth with little or no damage, then yes, they should fit your 9" Southbend. Would be handy if you could access a Southbend screwcutting chart to see what gears make a full set first though.
              'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

              Comment


              • #22
                Thread cutting info

                Commander,
                These links have SB manuals that have charts for gears for the A, B, C model lathes. This can help in determining what you have and what your wanting.
                The lead screw is 8tpi unless it is thread setup for metric.

                TX
                Mr Fixit for the family
                Chris



                https://www.google.com/url?sa=t&sour...bFgw3GDvbF6t2g

                https://www.google.com/url?sa=t&sour...GVDmuY4znOcf2A

                Comment


                • #23
                  You can cut threads that are multiples of the leadscrew pitch without a thread dial but not those which are a factor of the pitch. If you have an 8 pitch leadscrew and try to cut a 4 TPI thread, you will likely split it and cut a 2 start thread since you can engage the half-nuts every 1/8" along the screw. 1/8" off on multiple threads does not matter as you just skip one or more whole threads in your positioning.
                  Originally posted by becksmachine View Post
                  For purposes of practicing, if you pick a thread pitch that is an even multiple or divisor of the leadscrew pitch, you don't need to pay any attention to the thread dial.

                  If the lathe leadscrew is 6 tpi, you should be able to cut 6, 12, 24 and maybe 2, 3 threads per inch without even having a thread dial.

                  Dave
                  Don Young

                  Comment


                  • #24
                    I still suggest you first figure out what the gears you have will cut, select as coarse a thread as you can, and set up for that per the threading chart that should be riveted to the gear cover.

                    Then go ahead and cut threads, assuming that the coarsest thread is something no worse than 30 or 40 threads per inch,. You DO want to SEE the results, and also a coarser thread is less affected by slop in the system.

                    Actually, slop should be canceled out by just letting the carriage move a bit before it starts cutting. That should take up the slop, and ensure that you cut accurately.

                    That taking up of the slop is the reason for advancing the compound and not the crossfeed, as well as the 29 1/2 deg angle for the compound. The idea is to always have "pushback" via the cutting edge forces. Without that, on a lightweight lathe, there is a chance of the carriage being pulled forward, so that it is no longer following the leadscrew, the partly cut thread has "taken charge". The leadscrew should always push the carriage.

                    On a lathe with a heavy carriage, thatis much less of a problem, and consequently many folks who have never used an Atlas or other light lathe will tell you that the compound stuff is all hogwash.... because for them it is!
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #25
                      Originally posted by J Tiers View Post
                      the threading chart that should be riveted to the gear cover.
                      There ain't no gear cover.

                      I'm scouring the internet for parts as we speak. When I get what I need, I'll be back asking lots more questions.

                      Is it possible to retrofit a gear box to my lathe? By "possible" I mean bolt together, not heroic craftsmanship.

                      Comment


                      • #26
                        if you can find one, no problem

                        Comment


                        • #27
                          Commander,

                          This Yahoo site is a wealth of knowledge as well as the practical machinist site under the south bend subgroup, watch out for the rest of the site they frown on hobbiests with the simple questions.
                          Google is your friend when it comes to a topic like adding a QC box to a SB lathe. I have not done an add to a machine but there are others that have.

                          TX
                          Mr Fixit for the family
                          Chris

                          https://www.google.com/url?sa=t&sour...FI3emJuRXwniPA

                          Comment


                          • #28
                            Figured I'd throw this up here for the sake of completeness:

                            Many videos and a lathe purchase later, I've cut threads. The tool wasn't the right shape or even sharp enough, the lathe has a ton of slop in it and the lack of a thread dial and a clutch makes the process difficult, but those are all problems I can solve or live with.

                            Comment

                            Working...
                            X